1. Field of the Invention
The present invention relates to a new photosensitive resin composition, an ink jet head for discharging recording small liquid droplet used in an ink jet recording system and a method for manufacturing such an ink jet head.
More particularly, the present invention relates to an ink jet head manufacturing method in which a photosensitive resin layer contributing to formation of an ink flow path pattern is provided on a substrate for an ink jet head, and an ink jet recording head manufactured by such a manufacturing method.
2. Related Background Art
In general, an ink jet recording head (referred to merely as “head” hereinafter) for performing the recording by discharging ink comprises discharge ports for discharging the ink and ink flow paths which communicate with the respective ink discharge ports and within which pressure generating elements for generating pressure for discharging the ink are provided. Further, it is known to provide a head in which the pressure generating elements are formed on a substrate and ink flow path walls joined to the substrate to define the ink flow paths are provided. Among the heads, particularly, a head in which the ink discharge ports are disposed above the pressure generating elements is called as an ink jet head of side shooter type.
As a method for manufacturing such a head, U.S. Pat. Nos. 4,657,631; 5,331,344 and 5,458,254 disclose the following manufacturing method. That is to say, in the disclosed method, a soluble resin layer is provided on portions for defining ink flow paths and, in a condition that such a soluble resin layer is provided, the resin layer is coated by a coating resin layer which constitutes ink flow path walls later and then the soluble resin layer is removed.
In this manufacturing method, adhesive and the like are not dropped into the ink flow paths and a configuration of the ink flow paths can be formed with high accuracy. As the soluble resin layer, resist of positive type is used from the view point of easy removal. The resist of positive type serves to form a pattern on the basis of a difference in a dissolving speed between an exposed portion and a non-exposed portion, and, in any cases, the soluble resin layer corresponding to ink flow paths is dissolved and removed after exposure.
By the way, regarding such methods, the fact that formation of the coating resin layer provided on the ink flow path pattern and defining the ink flow path walls is performed by using a so-called solvent coat method is described. The solvent coat method is a method in which predetermined resin to be coated is dissolved in solvent and the resulting solvent is coated. As a representative solvent coat method, there is a spin coat method. Since the spin coat method has an advantage that a film thickness can easily be controlled uniformly, this method is frequently used in the method for manufacturing the head of side shooter type.
In a case where the coating resin layer constituting the ink flow path walls later is formed by the solvent coat method, since the resist of positive type is used as the soluble resin layer for the ink flow path pattern, the solvent must be selected carefully. That is to say, if a dissolving force of the solvent used in the solvent coat method is too strong, a non-exposed portion of the soluble resist of positive type may be partially dissolved by the solvent, with the result that the configuration of the obtained flow path pattern may be distorted.
By the way, in order to obtain a uniform film thickness of the film formed on the ink jet head substrate by the solvent coat method represented by the spin coat method, a vaporizing speed of the solvent and viscosity of the solvent must be adjusted. Particularly, in the ink jet head field, since such a film is normally formed to have a thickness considerably greater than a film thickness in a semiconductor field, it is difficult to make the film thickness uniform unless various film forming conditions are controlled more strictly in comparison with the films in the semiconductor field. Further, since the film thickness of the ink flow path pattern affects an influence upon an ink discharging property, the adjustment of the vaporizing speed and the viscosity affects a great influence upon through-put of the ink jet head. In particular, regarding the vaporizing speed of the solvent, the uniform film thickness can be achieved more easily in the solvent having slower vaporizing speed than in the solvent having higher vaporizing speed. However, in general, many of solvents having the slower vaporizing speed have a strong dissolving force which may distort the configuration of the ink flow path pattern, thereby causing a through-put problem. Thus, the solvent having the slower vaporizing speed does not necessarily contribute to the enhancement of productivity.